The steps for forming throughholes, wiring grooves, etc., employed in the process for production of semiconductor device are conducted using lithography. They are conducted ordinarily by forming a resist film, then conducting dry etching using the resist film as a mask, and then removing the resist film. Here, the removal of the resist film is conducted generally by plasma ashing and subsequent wet treatment using a stripping solution. As the stripping solution, various solutions have heretofore been developed and there are known, for example, organic sulfonic acid-based stripping solutions containing an alkylbenzenesulfonic acid as the main component, organic amine-based stripping solutions containing an amine (e.g. monoethanolamine) as the main component, and hydrofluoric acid-based stripping solutions containing hydrofluoric acid or a salt thereof as the main component.
Meanwhile, in recent years, low-resistance wiring materials such as copper have come to be used in response to the higher speed required for semiconductor elements, and it has become necessary that stripping solutions have anticorrosivity for wiring materials. The reason is that copper, as compared with conventional wiring materials such as aluminum, is inferior in anticorrosivity to stripping solutions and tends to corrode during a stripping step.
As a technique for preventing a metal film formed on a semiconductor substrate, from corroding, there is disclosed, in JP-A-7-247498, a technique for preventing corrosion of aluminum alloy by using, for cleaning after ashing, an aqueous solution containing a quaternary ammonium hydroxide, a saccharide or a sugar alcohol, and a urea compound. In this document is shown specifically a cleaning solution comprising tetramethylammonium hydroxide, sorbitol, urea and water. When a wiring is formed using an aluminum alloy film composed mainly of aluminum, steps are taken which comprise forming a photoresist of predetermined pattern on an aluminum alloy film and then dry-etching the aluminum alloy film using the photoresist as a mask. After the dry-etching, there is formed, on the side wall of the aluminum alloy film, a side wall-protecting film which is a product of reaction between the photoresist and the dry etching gas used. In this case, since a chlorine-based gas is generally used as the dry etching gas, there has been a problem that chlorine is taken into the side wall-protecting film and the aluminum alloy film is corroded after the completion of the etching. In the technique disclosed in JP-A-7-247498, it is described that the side wall-protecting film containing chlorine can be removed effectively by using a cleaning solution having the above-mentioned particular composition. This technique is intended to efficiently remove the chlorine-containing side wall-protecting film (which causes corrosion of aluminum alloy film) and improve the stripping performance of resist-stripping solution; however, the technique does not provide an anticorrosive agent which is effective for corrodible metals such as high-purity copper.
Meanwhile, a resist-stripping solution used for anticorrosion and cleaning of metal is disclosed in, for example, JP-A-8-334905. In this document, there are shown, as examples of anticorrosive agent, aromatic hydroxy compounds such as catechol, pyrogallol and hydroxybenzoic acid and carboxyl group-containing organic compounds such as acetic acid, citric acid and succinic acid. These anticorrosive agents, however, are intended to prevent corrosion of aluminum-copper alloys composed mainly of aluminum and have no sufficient anticorrosivity for high-purity copper of high corrodibility. In the above JP-A-8-334905 are disclosed, as other anticorrosive agents, benztriazole (BTA) and derivatives thereof. When this anticorrosive agent is used, certain anticorrosivity is obtained even to corrodible metals like copper.
BTA and derivatives thereof, however, are difficult to subject to biodegradation and the treatment of a waste solution containing them has been difficult. In recent years, a requirement for lower environmental load has become strong and higher safety has become necessary also for chemical substances used in factories producing semiconductor devices. Organic wastewaters generated in the factories are generally subjected to a biological treatment and, after decomposition, are discharged. Regarding substances incapable of being subjected to any biological treatment, it is desired to treat them using other means or change them to other chemical substance showing biodegradability. The above-mentioned TBA or derivatives thereof are extremely difficult to subject to the biological treatment. For the above reasons, in the factories using a stripping solution containing BTA or a derivative thereof, the waste solution or wastewater generated has had to be treated at a high environmental risk or by a method other than biodegradation, requiring a high cost and much labor.
In JP-A-9-291381 is described a conventional technique different from the present invention, that is, effectiveness of a urea condensation product as a water-soluble rust preventive. As examples of the urea condensation product, there are shown isocyanuric acid, hydantoin, uric acid, triscarboxymethylisocyanuric acid and triscarboxyethylisocyanuric acid. This technique, however, aims at rust prevention of metal during metal processing (e.g. cutting, polishing and plastic processing) and storage of worked metal and is not intended to provide a technique for removal of residue remaining in very fine holes and high-level surface cleaning, such as required in semiconductor device production. Further, the technique described in the above document aims at rust prevention of metal and has a task different from that (“anticorrosion”) of the present invention.
“Rust prevention” is to prevent the progress of oxidation of metal. In contrast, the “anticorrosion” aimed at in the present invention is to prevent corrosion of a metal film formed on a semiconductor wafer, specifically to prevent dissolution of metal (e.g. copper) or formation of metal complex, using a stripping component contained in resist-stripping solution. Treatment by rust preventive is conducted ordinarily in air and forms a protective layer made of rust preventive, on an oxide film present on a metal. In contrast, the “anticorrosion” of the present invention forms a protective layer on a clean metal surface not oxidized, by allowing an anticorrosive agent to act on the surface. A metal film formed on a semiconductor wafer, even when the surface has been oxidized (i.e. rusted) slightly, produces various problems such as increased resistance, insufficient adhesion with a film formed thereon, and the like. Therefore, the anticorrosive agent of the present invention is required to form a dense protective film on a metal film for substantially complete prevention of the oxidation of the metal film and further for effective prevention of the dissolution of the metal film and the formation of a metal complex both caused by a resist-stripping solution or a cleaning solution. That is, in the “anticorrosion” of the present invention is required a high-degree of metal film protectability rather than rust prevention. Further, as described later, the anticorrosive agent used in resist-stripping composition, unlike ordinary anticorrosive agents for metal members, is needed to have various properties. Thus, in designing a resist-stripping composition used in production of semiconductor device, an investigation must be made from standpoints different from those required in ordinary rust prevention of metals.